The present invention relates to a solid state imaging device and, in particular, to a signal charge transfer unit for transferring signal charges produced by a photoelectric conversion unit.
An imaging device having photoelectric conversion elements outputs light received from a photographing object as signal charges of the amount corresponding to the light amount using the photoelectric conversion elements and transfers the output signal charges to an image output circuit thereby outputs image signals.
A conventional solid state imaging device includes: a plurality of photoelectric conversion elements arranged on a semiconductor substrate in a one-dimensional or two-dimensional array and isolated by an isolation region; a plurality of read gate electrodes for reading signal charges obtained from the photoelectric conversion elements; a plurality of transfer gate electrodes for transferring the signal charges read by the read gate to a channel region; and a channel region for transferring the signal charges drawn into a channel region to another channel and an image output circuit.
The channel region includes a plurality of storage electrodes for storing the signal charges transferred through a transfer gate in a channel region and a plurality of barrier electrodes for transferring the signal charges stored in a semiconductor layer under the storage electrodes to a semiconductor layer under the storage electrodes adjacent thereto. The storage electrodes and barrier electrodes are alternately arranged perpendicularly to a transfer direction of signal charges. In addition, one of both end portions of the semiconductor layer under the storage electrode is connected to the transfer gate and the other is connected to a channel stop region. Signal charges are transferred by applying voltage pulses to the storage electrodes and the barrier electrodes so that the voltages under the electrodes are set to be higher than that in the vicinity thereof.
On the other hand, there has been known a solid state imaging device which transfers signal charges at high speed by forming storage electrodes and barrier electrodes obliquely to a transfer direction of signal charges so as to shorten a transfer distance of signal charges between the adjacent storage electrodes.
Further, Japanese Patent Application Laid-Open No. 2004-312664 has disclosed a solid state imaging device which includes channel regions of the same number as output channels and in which transfer electrodes for transferring signal charges between the channel regions are formed obliquely to a transfer direction toward an output direction of signal charges.
However, in such a channel region having a structure in which storage electrodes and barrier electrodes are arranged obliquely to a transfer direction of signal charges, a trajectory on which signal charges are transferred passes by a channel stop region or collides with the channel stop region. The reason is that signal charges are transferred perpendicularly to the obliquely arranged storage electrodes and barrier electrodes. Transfer with low-voltage pulses under such condition causes severe loss, and thus high-speed and highly efficient transfer of signal charges has been difficult.